12 Staff Protection Not place themselves in the primary beamUse of the inverse square lawUse of lead glass panelsUse of lead rubber coats/thyroid shields/lead glassesLimit of time spent in fluoroscopy: especially during pregnancyQA of the equipmentDose monitoring

14 X Ray Effects Stochastic – no threshold for damageNon stochastic – a quantifiable thresholdEffects can take place in somatic cells or be passed on (hereditary)

15 Stochastic EffectsProbability of the effect of radiation which can be either radiation induced cancers or genetic effects.No safe dose limitStatistically generatedLower doses of radiation

16 Non Stochastic EffectsAlso called deterministic effectsThere is usually a threshold below which the effect will not occurExamples are erythema (skin reddening) or epilation (hair loss)Doses are large eg following radiotherapy or as a result of a radiation accident (Chernobyl)

18 How are effects measured?• Sievert is unit of measurement – equivalent to a deposit of 1 joule of energy per kilogram mass of tissue• Relates dose absorbed in tissue to biological damage caused – “effective” dose• This will depend on the type of radiation• Typical background radiation results in an effective dose of 2.4 mSv/year

19 Additional risk of cancer per examExamples of DosesWe’re all exposed to background radiationChest = few daysSkull = few weeksSpine/Abdo = Few months or a yearCT Chest = few yearsAdditional risk of cancer per exam1 in 1,000 to 1 in 1,000,000Risk of cancer 1 in 3

20 Image production • Basic form uses photographic film• Denser structures attenuate the x-rays• When film is exposed to x rays it turns black• Image is contrast between two• Contrast can be manipulated using exposure factors and other aids such as contrast media

23 Factors affecting contrastTransmission – x-ray photons that pass through the patient unchanged.Absorbtion – x-ray photons that transfer their energy to the patient.Absorbtion is proportional to the degree of attenuation – thickness, density & atomic numberScatter – radiation that changes direction or is modified by decrease in energy as it passes through a bodyAttenuation – process that x-rays lose power as it travels through matter

32 CT explained Tomography tomos – slice graphia – describingWhere digital geometry processing is used to generate a three-dimensional image of the internals of an object from a large series of two dimensional x-ray images taken around a single axis of rotation.

33 CT in practice Data is obtained digitallyAlgorithms allow manipulation of dataWindowing is process of using a variety of Hounsfield UnitsSetting a top and bottom of range allows various tissue types to be imagedCan “get rid” of what you are not interested in

34 Magnetic Resonance ImagingThe latest imaging toolImages are similar in appearance to CT but produced without radiationTechnology utilises radio waves and a huge magnet to produce imagesThe magnet must be kept cool to allow superconductivity. It has to be cooled with liquid helium to -270 degrees.

39 Which Modality to use What are you attempting to image?What level of information do you wish to obtain?How do you wish to manipulate it?What protection measures need to be considered?

40 Radioisotope Imaging What is an isotope?Nuclei of atoms consist of protons and neutrons.The number of protons is called the atomic numberThe number of protons and neutrons is called the mass numberAll the atoms of one element with the same atomic number but different mass number are called isotopes

41 Radioisotopes Isotopes behave chemically the samesome of the radioisotopes will be radioactive ie emit radiationBy attaching these radioactive isotopes to certain pharmaceuticals we can use the emitted radiation to produce imagesMost commonly used isotope is Technetium99m because it decays by gamma emission

42 What is Radioactivity?Certain elements have isotopes which are unstableThe unstable atoms emit particles or energyThe particles or energy are radiationThe process is unpredictableIt is measured in Becquerels – 1 Bq is one “decay” event per second

44 Half LifeThe time taken for half of the atoms of a given sample to decayStays the same for a given isotope regardless of the actual quantityExpressed as a unit of timeCan be validated using experimentation and computer modeling

46 How does it work?Radioactive isotopes are labelled with pharmaceuticalsNow known as radiopharmaceuticalsIntroduced into the bodyPharmaceuticals influence tissue type which absorbs isotopeGamma emission is detected by a gamma cameraImage is digitally produced

47 Gamma Camera Detects individual Gamma photonsBuilds up an image over a period of several minutesUseful to show biological (metabolic) processes eg infections/secondary boney cancer deposits

48 Why do we use Nuclear Medicine?Radiopharmaceuticals do not cause much harm in proportion to benefit derivedBody will excrete materialRadioactivity is short lived – matter of hoursCan be used to image anatomy and physiologyCan be integrated with other modalities (PET)

49 Production Most useful isotopes are not naturalMust be produced by reactorsSide product of used nuclear fuelUsed uranium fuel has a content of molybdenum99Easily extractedTechnetium99 is a daughter productA few micrograms of molybdenum99 will produce enough technetium 99 to image 10,000 patients